Hitherto, conventional gaseous processes aimed at extending the shelf-life of materials prone to microbial spoilage have relied on modified atmosphere (MAP) procedures. In such procedures, the oxygen gas atmosphere surrounding the material is replaced with a food grade carbon dioxide and/or nitrogen atmosphere, and high barrier colaminate packaging is used to maintain the exclusion of oxygen from the package. The slight acidity produced by the carbonic acid which results from the exposure of the material to carbon dioxide produces a fungicidal effect. However, MAP processes have disadvantages. That is, whilst it has been found that an extension of the shelf-life is achieved in respect of materials treated by the procedures, this extension is limited and considerable costs are involved including the cost associated with the specialised colaminate film packaging used.
In copending U.S. patent application Ser. No. 08/771,400 (the entire disclosure of which is to be regarded as incorporated herein by reference), a method and apparatus is described for extending the shelf-life of materials prone to microbial spoilage by treating the materials with a volatile substance such as a natural food acid. The method described in this copending application involves prior evacuation of the vessel containing the material to be treated and, while this may lead to the more effective treatment of some materials, the inventors have now found that prior evacuation of the vessel containing the material is not necessary for the satisfactory extension of shelf-life.